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The construction of a hydroelectric plant causes irreversible social and environmental impacts

Dan Meyers image on Unsplash

The hydroelectric plant is formed by a set of works and equipment used to produce electric energy by taking advantage of the hydraulic potential existing in a river. This force is provided by the river's flow and the concentration of the existing unevenness along its course, which can be natural or built in the form of dams or through the river's diversion from its natural bed to the formation of reservoirs. Despite using a renewable energy source to generate electricity, a hydroelectric plant causes irreversible social and environmental impacts in the region where it is installed.

What is a hydroelectric plant?

The hydroelectric plant is an engineering work that uses the power of water to produce electricity. Also known as hydroelectric power plant or hydroelectric power station, it is a large structure that takes advantage of the movement of rivers to obtain electricity. However, the installation of a hydroelectric plant requires complex engineering works that cause several social and environmental impacts on the site.

How does a hydroelectric plant work?

To produce electricity in a hydroelectric plant, it is necessary to have an integration between the river flow, the unevenness of the terrain and the amount of water available. In short, the water that is stored in the reservoir is channeled and led to the large turbines. The flow of this water causes the turbines to rotate and activate the generators that will produce the electricity.

In this way, there is a transformation of mechanical energy, from the movement of water, into electrical energy. Once converted into electrical energy, transformers increase the voltage of this energy, allowing it to travel through transmission streams and reach establishments that need electrical energy.

The system of a hydroelectric plant is composed of:

Dam

The purpose of the dam is to interrupt the river's natural cycle, creating a water reservoir. In addition to storing this resource, the reservoir creates a water gap, captures water in an adequate volume for the production of electricity and regulates the flow of rivers in periods of rain and drought.

Water collection (adduction) system

This system is made up of tunnels, channels and metallic conduits that carry water to the powerhouse.

Powerhouse

It is in this part of the system that the turbines are located, connected to a generator. This instrument allows the movement of the turbines to convert the kinetic energy of water movement into electrical energy. There are several types of turbine, being pelton, kaplan, francis and bulb the main ones. The most suitable turbine for each hydroelectric plant depends on the head of fall and the flow of the river.

escape channel

After passing through the turbines, the water is returned to the natural river bed through the tailrace. The escape channel is located between the powerhouse and the river and its dimension depends on the size of the powerhouse and the river in question.

Spillway

The spillway allows the outflow of water if the level in the reservoir exceeds the recommended limits, which normally occurs in periods of rain. The spillway is opened when electricity production is impaired because the water level is above the ideal level; or to avoid overflows and flooding around the plant, common events in very rainy periods.

Types of hydroelectric plant

Run-of-the-river plant

To avoid the damage caused by the construction of traditional hydroelectric plants, run-of-river plants were created, a more sustainable option that does not use large water reservoirs, reducing the structure of dams and the dimension of flooding. In this model, the power of river currents is used to generate energy, without having to store water.

Plants such as Santo Antônio and Jirau, on the Madeira River, and Belo Monte, in Pará, have their structures based on the run-of-river concept. Even without large reservoirs, these plants maintain a minimum reserve to guarantee their operation and stability.

Despite having social and environmental advantages, the run-of-river plant reduces the country's energy security. That's because, in periods of prolonged drought, these structures can run out of water to generate electricity, since their reduced size reservoirs do not allow them to function for long periods.

According to specialists, an alternative to offset the limited potential of these plants is to invest in complementary sources. Thus, in periods when run-of-river hydroelectric plants operate with low capacity, energy generation through wind or solar sources can be used, ensuring supply and balancing the impacts caused by each one.

Plants with accumulation reservoirs

Hydroelectric power plants with accumulation reservoirs store water and regulate its operation to meet energy demands. The storage capacity is obtained through a dam located upstream of the plant and depending on its capacity there is talk of seasonal, annual and hyper-annual regulation.

Hydroelectric Power Plants in Brazil

Brazil is the third largest producer of hydroelectric energy in the world, after Canada and the United States. In addition, it is also the third country with the greatest hydraulic potential, behind Russia and China. About 90% of the electricity generated in Brazil comes from hydroelectric plants.

There are just over 100 hydroelectric plants spread across Brazil. Among them, five stand out for their capacity to generate electricity:

• Itaipu Binacional Hydroelectric Power Plant: located on the Paraná River, it covers part of the state of Paraná and part of Paraguay;
• Belo Monte Hydroelectric Power Plant: located on the Xingu River, in Pará;
• Tucuruí Hydroelectric Power Plant: located on the Tocantins River, also in the state of Pará;
• Jirau Hydroelectric Power Plant: located on the Madeira River, in Rondônia;
• Santo Antônio Hydroelectric Power Plant: located on the Madeira River, also in Rondônia.

Curiosities

• The largest hydroelectric power plant in the world is the Three Gorges Plant, located in China;
• The American Society of Civil Engineers (ASCE) considered the Itaipu Power Plant one of the "Seven Wonders of the Modern World". It is the second largest hydroelectric plant in the world and produces 20% of Brazilian demand and 95% of Paraguayan electricity demand;
• About 20% of the electricity produced worldwide comes from hydroelectric power plants.

Social and environmental impacts of a hydroelectric plant

Although hydroelectric energy is considered a renewable energy source, the Aneel report points out that its participation in the world electric matrix is ​​small and is becoming even smaller. Such growing lack of interest would be the result of negative externalities arising from the implementation of projects of this size, according to the report.

One of the negative impacts of the implementation of a hydroelectric plant is the change it causes in the way of life of the populations that reside in the region. It is important to emphasize that these communities are often human groups identified as traditional populations (indigenous peoples, quilombolas, Amazonian riverside communities and others), whose survival depends on the use of resources from the place where they live, especially rivers, and who have links cultural order with the territory.

Is the energy generated at the hydroelectric plant clean?

Despite being considered a clean energy source, hydroelectric power generation contributes to the emission of carbon dioxide and methane, two gases that intensify global warming.

The emission of carbon dioxide (CO2) is due to the decomposition of trees that remain above the water level in the reservoirs, and the release of methane (CH4) occurs through the decomposition of organic matter present at the bottom of the reservoir. As the water column increases, the concentration of methane (CH4) also increases. When water hits the plant's turbines, the difference in pressure causes the methane to be released into the atmosphere. Methane is also released into the water's path through the plant's spillway, when, in addition to the change in pressure and temperature, the water is sprayed in droplets.

As methane is not incorporated into photosynthesis processes, it is considered more harmful to global warming compared to carbon dioxide. This happens because a large part of the carbon dioxide emitted is neutralized through absorptions that occur in the reservoir.

Damage to fauna and flora

The main impacts of the construction of a hydroelectric plant on the local fauna and flora are:

• Destruction of natural vegetation;
• Sedimentation of river beds;
• Breakdown of barriers;
• Extinction of fish species, due to interference in migratory and reproductive processes (piracema);
• Acidification of water when the area to be used for the plant's reservoir is not properly cleaned;
• Losses of native aquatic and terrestrial flora and fauna;
• Occurrence of seismic activities due to the weight of water on the underlying rock substrate;
• Changes in the water in the reservoir related to temperature, oxygenation (dissolved oxygen) and pH (the occurrence of acidification);
• Water pollution, contamination and introduction of toxic substances into reservoirs due to the flow of pesticides, herbicides and fungicides from pre-existing plantations in the flooded region;
• Introduction of exotic species in the reservoirs, out of balance with the hydrographic basin ecosystems;
• Removal of riparian forest;
• Increased predatory fishing, by professional fishermen or in leisure activities;
• Implementation of a physical barrier that prevents seasonal migrations of species, disturbing the balance of the ecosystem;
• Decrease in carbon sequestration by flooded vegetation, contributing to increase the greenhouse effect.

soil loss

The soil in the flooded area will necessarily become unusable for other purposes. This becomes a central issue in predominantly flat regions such as the Amazon region. Since the power of the plant is given by the relationship between the flow of the river and the unevenness of the land, if the land has a low unevenness, a greater amount of water must be stored, which implies an extensive reservoir area.

Changes to the hydraulic geometry of the river

Rivers tend to have a dynamic balance between discharge, average water velocity, sediment load and bed morphology. The construction of reservoirs affects this balance and, consequently, causes changes of a hydrological and sedimentary order, not only in the impoundment site, but also in the surrounding area and in the bed below the reservoir.

In this way, the formation of hydroelectric power plant reservoirs generally affects more fertile soils and arable land, disintegrating the local population, which loses its historical characteristics, cultural identity and its relations with the place, in addition to the alteration in aquatic ecosystems and the destruction of flora and of fauna.